Magnetron plasma processing apparatus and processing method

ABSTRACT

A magnetron plasma processing apparatus includes, a vacuum chamber storing an etching object, a first electrode which is provided in the vacuum chamber and holds the etching object, a second electrode which is disposed in opposition from the first electrode and parallel with the first electrode. A gas-supply unit feeding etching gas to the vacuum chamber while, a magnetic-field generating means is disposed on the part opposite from the first electrode in opposition from the second electrode, and a power-supply unit feeds power to either the first or second electrodes and generates discharge between the electrodes. The magnetic-field generating means is provided with a magnetic block whose both-end surfaces are provided with magnetic poles having polarity inverse from each other, and in addition, a plane recess opposite from the second electrode is provided between both-end surfaces of the magnetic block.

This is a division of application Ser. No. 07/766,324, filed on Sep. 27,1991, now U.S. Pat. No. 5,362,352.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetron plasma processing apparatusand a method of processing magnetron plasma available for the productionof semiconductor integrated circuits.

2. Description of the Related Art

Any conventional magnetron plasma etching or dry etching apparatus as anexample of magnetron plasma processing apparatus generates electricfield between parallel plane electrodes and magnetic field orthogonallyintersecting the electric field. Such a conventional magnetron plasmaetching apparatus executes an etching process against a semiconductorrefer by generating plasma with etching gas to process this wafermounted on one of those plane electrodes.

Normally, in order to promote anisotropy as the typical etchingcharacteristic, such a conventional magnetron plasma etching apparatuscited above executes an etching process by maintaining the internalpressure of vacuum chamber very low like 3.5 m Torr, or 7 m Torr, or 9 mTorr, for example.

Although anisotropy is securely promoted in the course of etching thesemiconductor wafer by holding the internal pressure of the vacuumchamber very low as cited above, the etching rate can hardly bemaintained at a constant level on the semiconductor wafer. Inventors ofthe invention detected that application of such low internal pressure tothe etching process of semiconductor wafer resulted in the generation offaulty shape of the wafer itself like the bent or gouged configuration.After exploration of the cause of these faulty symptoms, inventorsconfirmed that, when such low pressure was applied, due to leastprobability of generating collision between ions, plasma remained in lowdensity, thus resulted in the generation of comparatively thick plasmasheath (in other words, dark sphere of plasma) in the neighborhood ofthe semiconductor wafer.

Based on this discovery, inventors further detected that, after beingreleased from the semiconductor wafer as a result of generatingcollision between electrons, secondary electrons performed cyclonicmovement according to the relationship between electric field andmagnetic field, and then, even when the secondary electrons weresupposed to traverse plasma, the secondary electrons shifted themselvesto one side without hitting against gas seeds, but instead, thesecondary electrons moved themselves into the comparatively thick plasmasheath without traversing plasma at all, and finally, cumulatedthemselves on the peripheral edges of the semiconductor wafer.

Taking these symptoms into account, inventors finally confirmed thatplasma could not maintain uniform density in the neighborhood ofsemiconductor wafer, and yet, cumulated electrons adversely affected theetching characteristic.

Such a conventional magnetron plasma etching system has anothertechnical problem to solve. Concretely, due to uneven intensity anddirection of magnetic field, etching process cannot properly be executedat minimum etching speed, and in addition, ions cannot hold owndirectivity constant, but these ions are obliged to obliquely enter intothe wafer substrate, thus eventually making it difficult for thisconventional to properly execute the etching process with satisfactoryanisotropy.

Although not strictly being defined, a variety of physical reasons areassumed to adversely affect the etching process to result in the poorformation of the semiconductor wafer. More particularly, line ofmagnetic force formed in the peripheral edges of the semiconductor wafercannot be formed in parallel with the upper surface of the semiconductorwafer, but instead, it turns into loop. Since electric field remainscomparatively less in plasma, electrons are subject to intense influenceof magnetic field, and as a result, electrons respectively performspiral movement with a circle of about 2 mm across by way of surroundingthe line of magnetic force. As a result, when the line of magnetic forceintersects the semiconductor wafer, electrons obliquely enter into thewafer along the line of magnetic force.

On the other hand, those ions directly being applied to the etchingprocess respectively contain substantial mass, and thus, these ions arerarely subject to deviation of their moving direction otherwise causedby direct influence of magnetic field. Nevertheless, when electronsobliquely enter into semiconductor wafer substrate under process, theseelectrons merely collide with one-side wall of the substrate to resultin the uneven cumulation of charge on both-side walls, which in turngenerates uneven and asymmetrically distributed charge. In consequence,new electric field is generated on both sides of the semiconductor wafersubstrate, which then affects ions so that ions are obliged to move onthemselves in deviant directions. This eventually results in thedegraded anisotropy in the formation of semiconductor wafers.

To solve this problem, if a plurality of permanent magnets were providedon both ends of parallel plane electrodes consisting of substrateelectrodes and opposite electrodes, the upper surface of thesemiconductor wafer will be provided with specific magnetic field whichapproximates parallel. In this case, the conventional magnetron plasmaprocessing apparatus can generate such a semiconductor wafer containingsatisfactory anisotropy. On the other hand, when disposing a pluralityof permanent magnets on both sides of parallel plane electrodes, becauseof positionwise relationship, it is extremely difficult for the systemto rotate those permanent magnets. Furthermore, no art can materializeuniform etching effect without rotating those permanent magnets.Furthermore, in order to generate uniform magnetic field on thesemiconductor wafer based on the structure cited above, the system needsto provide large size permanent magnets.

There is such a conventional apparatus under a proposal which disposescoil-like electrodes in the periphery of the vacuum chamber in place ofthose permanent magnets mentioned above. The proposed apparatus ischaracteristically capable of rotating the direction of magnetic fieldby feeding alternate current having phases 90° apart from each other tothe two pairs of coils orthogonally intersecting each other.

On the other hand, in order to uniformly feed magnetic field to thewhole surface of the semiconductor wafer, these coils must respectivelyhave substantial diameter in proportion to the dimcnoiono of the vaccumchamber. In other words, the greater the dimension of the semiconductivewafer, the greater the dimension needed for the coils. this in turnrequires the power supply source to increase the power supply capacity.Furthermore, since the magnetic field intensely affects both theinterior and exterior of the chamber including unwanted domain, theproposed magnetron plasma processing system cannot practically use suchelectronic elements which are extremely sensitive to magnetism, and yet,the proposed system needs to any effective means to prevent magnetismfrom leaking out of the apparatus.

SUMMARY OF THE INVENTION

The primary object of the invention is to uniformly level off theetching rate covering the whole surface of the semiconductor wafer underprocess by evenly generating plasma all over the surface of thesemiconductor wafer under process so that the form of the semiconductorwafer complete with the etching process can be improved.

The second object of the invention is to minimize leakage of magneticfield from the magnetron plasma processing apparatus embodied by theinvention.

To achieve the primary object of the invention, a novel magnetron plasmaprocessing apparatus is provided by the invention, whichcharacteristically comprises the following; a vacuum chamber whichstores a semiconductor wafer under process; a pair of parallelelectrodes comprising the first electrode which is provided in thevacuum chamber to hold the semiconductor wafer under process and thesecond electrode which is disposed in opposition from the firstelectrode; a gas-supply means which supplies gas to the vacuum chamber;a magnetic-field generating means which is disposed to the side oppositefrom the first electrode installed in opposition from the secondelectrode, wherein said magnetic-field generating means is provided witha magnetic block containing magnetic poles inverse from each other onboth-end surfaces, and yet, a recess is provided between these endsurfaces by way of being opposite from the second electrode; and apower-supply means which feeds power to either of the first and secondelectrodes to generate discharge between these parallel planeelectrodes.

Likewise, to achieve the primary object of the invention, anothermagnetron plasma processing apparatus is hereby provided, whichcharacteristically comprises the following; a vacuum chamber whichstores a semiconductor wafer under process; a pair of parallelelectrodes comprising the first electrode which is provided in thevacuum chamber to hold the semiconductor wafer under process and thesecond electrode which is disposed in opposition from the firstelectrode; the third electrode which is disposed by way of surroundingthe first electrode and grounded; a gas-supply means which feeds gas tothe vacuum chamber; a magnetic-field generating means which is disposedto the side opposite from the first electrode in opposition from thesecond electrode and generates magnetic field between these parallelelectrodes; and a power-supply means which feeds power to either of thefirst and second electrodes to generate discharge between those parallelelectrodes described above.

Furthermore, to achieve the primary object of the invention, anothermagnetron plasma processing apparatus is provided, whichcharacteristically comprises the following; a vacuum chamber whichstores a semiconductor wafer under process; a magnetic-field generatingmeans which generates magnetic field by way of substantially being inparallel with the upper surface of the semiconductor wafer underprocess; a plasma-generating means which generates electric fieldorthogonally intersecting the upper surface of the semiconductor waferunder process, and yet, generates plasma in the vacuum chamber; and aninternal pressure adjusting means which properly adjusts pressure insideof the vacuum chamber in a range from 10 m Torr to a maximum of 100 mTorr.

To achieve the primary object of the invention, a novel method ofexecuting magnetron plasma processing operation is also provided by theinvention, which includes the following sequential steps of; feeding gasto a vacuum chamber, followed by adjusting pressure of the supplied gasto a predetermined degree above 10 m Torr; mounting a semiconductorwafer on the first electrode secured inside of the vacuum chamber;generating magnetic field by way of substantially being in parallel withthe upper surface of the semiconductor wafer in the neighborhood of thefirst electrode via a magnetic-field generating means which is disposedon the back of the second electrode in opposition from the firstelectrode; and generating electric field between the first and secondelectrodes to generate discharge before eventually processing thesemiconductor wafer with plasma.

To achieve the second object of the invention, a novel magnetron plasmaprocessing apparatus is hereby provided, which characteristicallycomprises the following; a vacuum chamber which stores a semiconductorwafer under process; a gas-supply means which supplies gas to the vacuumchamber; a plasma-generating means which generates electric field by wayof orthogonally intersecting the upper surface of the semiconductorwafer under process to generate plasma in the vacuum chamber; amagnetic-field generating means which generates magnetic field by way ofsubstantially being parallel with the upper surface of the semiconductorwafer under process held in the vacuum chamber; a compensatorymagnetic-field generating means which is opposite from the vacuumchamber, wherein said compensatory magnetic-field means generatesmagnetic field in the direction opposite from that is generated by saidmagnetic-field generating means; and a means for rotating magnetic fieldgenerated by said magnetic-field generating means and said compensatorymagnetic-field generating means.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 schematically designates block diagram of the magnetron plasmaprocessing apparatus (which is substantially an etching apparatus)according to the first embodiment of the invention;

FIGS. 2A and 2B respectively designate the bottom surface (2A) and thevertical sectional view (2B) in the longitudinal axial direction of apermanent magnet shown in FIG. 1;

FIGS. 3A through 3C respectively designate sectional views showingaspects of resist etching in the multi-layer resist forming process toexplain the magnetron plasma processing method (which is substantiallyan etching method) according to an embodiment of the invention;

FIG. 4 graphically designates the relationship between magnetic fieldgenerated by permanent magnets and the etching characteristic;

FIGS. 5A and 5B respectively designate aspects of discharge generatedbetween electrodes;

FIG. 6 graphically designates distribution of the etching speed inpresence of 50 m Torr of gas pressure;

FIG. 7 graphically designates the relationship between the uniformity ofthe etching speed and the gas pressure when rotating permanent magnets;

FIG. 8 graphically designates the distribution of the etching speed inthe direction orthogonally intersecting the line of magnetic force whensecuring permanent magnets;

FIGS. 9A and 9B respectively designate lateral views of the samplesetched by rotating permanent magnets;

FIGS. 10A and 10B respectively designate sectional views of gateelectrodes of MOS LSIs processed by the etching method embodied by theinvention;

FIG. 11 graphically designates the etching speed in those cases whenthose electrodes having a variety of dimensions are introduced to theetching apparatus shown in FIG. 1;

FIGS. 12 and 13 schematically designate distribution of plasma sheathgenerated between electrodes;

FIG. 14 graphically designates the distribution of the etching speed ona semiconductor wafer after varying gas pressure inside of the vacuumchamber;

FIGS. 15A through 15D respectively designate sectional views showinggouged condition of the etched domain caused by varied gas pressureinside of the vacuum chamber;

FIGS. 16A through 16C respectively designate sectional views showing theaspects of the improved effect of the etched domain as a result ofvarying the gas pressure in the vacuum chamber;

FIG. 17 graphically designates the relationship between self-biasvoltage of the secondictor wafer and the gas pressure;

FIG. 18 schematically designates an experimental apparatus analyzing therelationship between the direction of the line of magnetic forcegenerated between electrodes of the etching apparatus shown in FIG. 1and the form of the etched domain;

FIG. 19 graphically designates the relationship between the form of theetched domain in the center of the wafer and the angle of inclinedpermanent magnets against the surface of electrodes;

FIG. 20 schematically designates the block diagram of the magnetronplasma processing (etching) apparatus according to the second embodimentof the invention;

FIG. 21 schematically designates the block diagram of the magnetronplasma processing (etching) apparatus according to the third embodimentof the invention;

FIG. 22 designates a lateral view of a modified permanent magnetintroduced to the magnetron plasma processing apparatus shown in FIG.21;

FIG. 23 designates a perspective view of magnetic element composing apermanent magnet;

FIG. 24 schematically designates the line of magnetic force of apermanent magnet;

FIG. 25 designates a partial view of another modified permanent magnet;

FIG. 26 graphically designates the distribution of magnetic field on asemiconductor wafer;

FIG. 27 designates lateral view of the semiconductor wafer and apermanent magnet explanatory of FIG. 26;

FIG. 28 designates a lateral view of a permanent magnet explanatory ofFIG. 29;

FIG. 29 graphically designates the relationship between the distancefrom the center of the magnet and the leaked magnetic flux;

FIG. 30 graphically designates the relationship between the distancebetween magnet elements and the leaked magnetic flux;

FIG. 31 designates a lateral view of a permanent magnet explanatory ofFIG. 30;

FIG. 32 graphically designates the relationship between the distancebetween magnetic elements and the magnetic flux density in the center ofthe semiconductor wafer; and

FIG. 33 designates a lateral view of a permanent magnet explanatory ofFIG. 32.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, the magnetic plasmaprocessing apparatus and the related method embodied by the inventionare respectively described below.

FIG. 1 schematically designates the block diagram of the dry-etchingapparatus which is substantially the magnetic plasma processingapparatus according to the first embodiment of the invention. Thedry-etching apparatus is provided with a vacuum chamber 20 which iscapable of materializing vacuum up to 10⁻⁶ Torr for example. The vacuumchamber 20 is internally provided with a bottom electrode 22 which ismounted on a supporting table 23b via an insulator 23a.

An upper electrode 24 is substantially composed of the top wall of thevacuum chamber 20, where the upper electrode 24 is disposed above and inopposition from the bottom electrode 22. The bottom electrode 22 and theupper electrorode 24 conjunctionally make up a unit of parallel planeelectrodes A thermo-control means (not shown) and an electrostatic chuck(not shown) are respectively provided fro the bottom electrode 22. Theelectrostatic chuc secures a semiconductor wafer 14 on the upper surfaceof the bottom electrode 22, where the difference of temperature betweenthe secured semiconductor wafer 14 and the bottom electrode 22 is heldat a maximum of 5° C. The superficial area which dose not secure thesemiconductor wafer 14 is covered by conductive material or insulatingmaterial having less than 1 mm of thickness. An inlet 20a is providedfor the vacuum chamber 20 to introduce etching gas, which is connectedto an etching-gas supply unit 21. In other words, the etching-gas supplyunit 21 supplies etching gas containing predetermined pressure to theinterval between the parallel plane electrodes.

The bottom electrode 22 is connected to a high-frequency power-supplysource 28a via a capacitor 29 and grounded via a switch 26a. The upperelectrode 24 is selectively connected to the ground or thehigh-frequency power-supply source 28b via a switch 26b. Therefore, themagnetron plasma processing apparatus of the first embodiment of theinvention can execute a plasma etching process by optionally selectingeither the anode-coupling (PE) system or the cathode-coupling (RIE)system. Concretely, when connecting the high-frequency powersupplysource 28b to the upper electrode 24 and grounding the bottom electrode22, the magnetron plasma processing apparatus of the first embodimentoperates itself based on the anode-coupling system. Conversely, whenconnecting the high-frequency to the bottom electrode 22, the magnetronplasma processing apparatus operates itself based on thecathode-coupling system. A permanent magnet 30 having a stepped recess32 is held by an aluminium-made non-magnetic magnet holder 34 above theupper electrode 24. The permanent magnet 30 is subject to rotation bythe force driven by a non-magnetic rotary shaft 36 connected to themagnet-holder 34.

Next, referring to the bottom view and the sectional view shown in FIGS.2A and 2B, structure of the permanent magnet 30 is described below.

A pair of stepped recesses 32 are provided on the surface of thepermanent magnet 30 which is opposite from the upper electrode 24, wherethese stepped recesses 32 respectively make up the lateral walls of thepermanent magnet 30 on both sides in the magnetizing direction. Thesestepped recesses 32 are respectively provided with stepwise depth whichis deeper in the direction of the Center from both sides. As Shown inFIG. 2A, the permanent magnet 30 is of elliptic shape, which ismagnetized in the longitudinal axial direction, where the S-pole isformed on the external surface of an end of the magnetizing direction,whereas the N-pole is formed on the external surface of the other end.Structurally, the permanent magnet 30 introduced to the magnetron plasmaprocessing apparatus of the first embodiment is composed of a number offerrite pieces which are tightly assembled into the shape shown in FIG.2 before being magnetized in the longitudinal axial direction.

The first embodiment provides 4-step wall members on both sides of thestepped recesses 32 of the permanent magnet 30 including the first wallmember 40, the second wall member 42, the third wall member 44, and thefourth wall member 46, which respectively have differential steps in thevertical direction. Of these, as shown in FIG. 2A, stepwise notch 48 isprovided for the outermost first wall member 40 so that distance betweenthe first wall members 40 and 40 can be contracted in the direction ofboth sides of the longitudinal axis of the permanent magnet 30. Thesefirst wall members 40 and 40 are respectively provided in order toprevent the intensity of magnetic field from declining itself when thepermanent magnet 30 leaves the longitudinal axis in the widthwisedirection. These first through fourth wall members are respectivelyprovided with magnetic poles inverse from that of the back surface ofthe permanent magnet 30.

Next, functional operation of the dry etching apparatus according to thefirst embodiment of the invention is described below.

As a whole, there are three kinds of the line of magnetic forcegenerated in the permanent magnet 30 containing the stepped recesses 32.The first line of magnetic force has substantial curvature and isgenerated between the inner and outer surfaces of the first wall members40. The first line of magnetic force is generated in the neighborhood ofthe tip surface of the first wall members 40 without adversely affectingthe magnetic field on the semiconductor wafer 14 which is apart from thesurface of the permanent magnet 30 by 52 cm for example.

The second line of magnetic force is generated between the oppositesurfaces of those wall members 40 through 46, where majority of thesecond line of magnetic force is formed in the stepped recesses 32 ofthe permanent magnet 30, and yet, like the first line of magnetic force,the second line of magnetic force is free from adversely affecting themagnetic field present in the neighborhood of the semiconductor wafer14.

On the other hand, the third line of magnetic force is generated on theexternal surface on both sides of the permanent magnet 30 in themagnetizing direction, thus generating magnetic field at a positionopposite from the semiconductor wafer 14. The drying etching apparatusaccording to the first embodiment makes use of the third line ofmagnetic force in the form of parallel magnetic fields against thesemiconductor wafer 14.

When electrons spin themselves by way of pivoting the third line ofmagnetic force and then fly in the tangential direction, electronssymmetrically enter into grooves of the wafer under process, thusachieving an etching process with satisfactory anisotropy. Inparticular, inventors confirmed that satisfactory etching process withimproved anisotropy was achieved by generating the third line ofmagnetic force in parallel with the dark discharge domain (which issubstantially sheath region) generated in the neighborhood of the wafer14. Furthermore, inventors confirmed that the dry etching apparatusbased on the first embodiment of the invention securely maintained fluxdensity substantially at 100 G on the whole surface of the wafer 14 byapplying the permanent magnet 30 made from inexpensive ferrite pieces,and yet, the apparatus securely generated parallel magnetic field whichwas intense enough to execute the predetermined magnetron etchingprocess.

Furthermore, since the magnetron etching apparatus of the firstembodiment of the invention installs the permanent magnet 30 on the backof the upper electrode 24, the permanent magnet 30 can be set to aspecific position apart from the position which is solely available forloading and unloading the wafer 14 into and out of the magnetron etchingapparatus. This in turn permits manufacturers to easily introduce auseful structure capable of rotating the permanent magnet 30. In thisway, the magnetron etching apparatus of the first embodiment can rotatethe parallel magnetic field on the upper surface of the wafer 14 byrotating the permanent magnet 30. AS a result, intensity of the parallelmagnetic field can uniformly be distributed on the whole surface of thewafer 14, thus making it possible for the magnetron etching apparatus ofthe first embodiment to achieve the uniformity of the etching rate onthe whole surface of the wafer 14.

The first embodiment of the invention does not restrain the scope of therecesses formed in the permanent magnet 30 solely to the four-steprecesses 32, but single-step recesses may also be made availableprovided that the permanent magnet 30 be of modest dimension. However,according to the result of trials executed by inventors, it wasconfirmed that the provision of multiple-step recesses was by faradvantageous to generate uniformly parallel magnetic field compared tothe provision of single or double step recesses. It is thereforeprobable that the provision of multiple-step recesses securely promotesthe effect of confining the first and second lines of magnetic force inthe neighborhood of the permanent magnet 30 or in those multiplie-steprecesses 32, thus generating uniformly parallel magnetic field.Furthermore, the first embodiment does not always restrain the scope ofthe recess in the permanent magnet 30 solely to those which are subjectto the stepwise change of depth of the recesses, but the firstembodiment may continuously vary the depth of the recesses by providingsloped inner surface of the recesses. However, taking the processingconvenience into account in the case of assembling small ferrite piecesto compose the permanent magnet 30, manufacturers can more easilyproduce the permanent magnet 30 incorporating stepped recesses.

Next, taking resist etching in the multiple-layer resist formationprocess for example, the method of executing the etching process againstsemiconductor wafer 14 by applying the magnetron plasma etchingapparatus embodied by the invention is described below.

The multiple-layer resist formation process is substantially a means forpreserving extremely high lithographic precision on the unlevelledsurface of the substrate comparable to the lithographic precision on aplane. Triple-layer resist formation process is the typical of themultiple-layer resist formation process. Initially, substrate surfacewith stepwise differential levels is coated with resist to level off thesurface once. Next, an intermediate layer composed of inorganic compoundfilm like "spin-on-glass (SOG)" is formed on the level surface. Next,predetermined patterns are thermally provided by applying a conventionallithographic process. Next, the predetermined patterns are eventuallyformed by sequentially etching the SOG film and the resist by applying areactive ion etching process.

As shown in FIG. 3A by means of the sectional view of the wafer underprocess, the semiconductor wafer 14 made available for the firstembodiment comprises triple layers built on the substrate 80 includingthe first resist layer 81, the etching-completed SOG layer 82, and thetop resist layer 83.

Initially, inventors supplied oxygen containing constant pressure intothe vacuum chamber 20 of the dry etching apparatus shown in FIG. 1, andthen induced discharge by applying the cathode-coupling system afterfeeding 13.56 MHz of RF power to the bottom electrode 22 mounting thesemiconductor wafer 14 before executing a predetermined etching process.

First, in order to make sure of the relationship between magnetic fieldgenerated by the permanent magnet 30 shown in FIG. 1 and the etchingcharacteristic, inventors analyzed the distribution of the etchingvelocity by holding the permanent magnet 30 still. FIG. 4 graphicallydesignates the distribution of the etching velocity when applying 3.5 mTort of oxygen pressure. More particularly, FIG. 4A graphicallydesignates the distribution of the etching velocity in the direction ofthe line of magnetic force, in which the etching velocity is almostsymmetrically distributed despite of slight rise in the peripheralregions against the center position. On the other hand, the etchingvelocity in the direction orthogonally intersecting the line of magneticforce shown in FIG. 4B is asymmetrically distributed with the indicationof monotoneous increase in the leftward direction.

After completing visual analysis of the section of the etched shape, asshown in FIG. 3B, inventors confirmed that the resist domain section 84with fine repeated patters was verticallt etched. On the other hand, theother resist domain section 85 facing a broad groove incurredconstriction on the side wall which was set in the direction of fasteretching velocity. The etching velocity was leveled off by rotating thepermanent magnet 30. Nevertheless, inventors also confirmed that theetching velocity in the center and the peripheral regions of the waferwas not properly leveled off. In particular, inventors confirmed thatthe etching velocity was significantly uneven in the peripheral regionsof the wafer in contrast with the center. Although the etched shape wassymmetrically formed on both sides as a result of the rotation of thepermanent magnet 30, side wall oriented in the faster etching velocitystill incurred constriction.

When magnetron discharge is generated, due to the effect of electricfield which is mainly generated between cathode and plasma and theeffect of magnetic field orthogonally intersecting the generatedelectric field, electrons continuously perform cycloidal movement in thedirection of orthogonally intersecting the generated electric field andmagnetic field. This phenomenon effectively promotes density of plasmarelative to the increased rounds of collision between electrons andoxygen molecules. Simultaneously, this phenomenon also generatesgradient of the density of plasma between surfaces of those electrodesin the direction orthogonally intersection magnetic field, thuseventually generating uneven etching velocity and asymmetrically etchedshape of side wall of the wafer.

Although irregularity of the etching velocity can be eliminated byproviding a concentrically circular maget which permits electrons tofollow up circulating movement by closing the route of electrons toperform cycloidal movement, this method still generates uneveness of theetching velocity between the electron rout and other domains.Furthermore, such a concentrically circular magnet cannot fully suppresshorizontal magnetic field.

As is clear from the above description, gradient of the density ofplasma dominantly causes the etching velocity and the processed shape tolose evenness. Therefore, advantageous feature of the magnetron etchingapparatus embodied by the invention can fully be materialized byeffectively suppressing generation of the gradient of the plasmadensity. Taking this into account, inventors carried out trials to checkthe influence of gas pressure gravely affecting the uniformity of thedensity of plasma.

On the way of visual analysis of the state of discharge in the directionorthogonally intersecting the line of magnetic force, as shown in FIG.5A, when the gas pressure was held at 3.5 m Torr, an outwardly projectedregion beyond an edge of an electrode 90 emitted intense luminance. Itis probable that the projected region 91 generated intense luminance asa result of the concentrated effect of electrons which continuouslyperformed drifting movement on the electrode 90. Thus, inventors againvisually analyzed the state of discharge in the direction orthogonallyintersecting the line of magnetic force by raising gas pressure to 25through 50 m Torr. As a result, inventors then confirmed that, as shownin FIG. 5B, sheath region 92 having several millimeters of lengthmatching the whole length of cathode generated intense luminance, thusresulting in the sharply improved uniformity of discharge in thecathode. In presence of the increased gas pressure, gas molecules morefrequently collide themselves with those electrons on the electrode 90on the way of drifting themselves after completing cycloidal movement.In consequence, density of plasma is stabilized in a relatively shortdistance to vary the state of discharge.

FIG. 3C designates the sectional view of the resist shape aftercompleting an etching process by applying the magnetron etchingapparatus shown in FIG. 1. Using this apparatus, inventors executed anetching process against a semiconductor wafer having 150 mm of diameterby feeding 50 sccm of oxygen gas and 600 W of RF power. As a result,constriction on the side wall shown in FIG. 3B was fully eliminated fromthe one shown in FIG. 3C, thus achieving complete shape withsatisfactory anisotropy.

After fully analyzing the relationship between the etched shape and theapplied gas pressure, inventors confirmed that the asymmetricalconstriction on the side wall diminished to a practically admissiblerange, in other words, to a maximum of 5000 Å as a result of applying aminimum of 25 m Torr of gas pressure. Inventors thus confirmed thatthere was a certain relationship between the visually checked dischargedistribution and the constriction generated on the side wall of thewafer. Inventors further discovered that, when applying more than 125 mTorr of gas pressure, since ions actively scattered themselves,constriction noticeably occurred on the side wall independent of thedirection and the width of pattern.

FIG. 6 graphically designates the distribution of the etching velocity.Curve (a) designates the direction of the line of magnetic force,whereas curve (b) designates the distribution of the etching velocityorthogonally intersecting the line of magnetic force. There is aconstant tendency in the curve (b) to continuously rise itself in theleftward direction. However, as a whole, the etching effect and theuniformity respectively indicate substantial improvement.

FIG. 7 graphically designate the relationship between the uniformity ofthe etching velocity and the discharge pressure. The difference betweenthe maximum value and the minimum value was divided by the mean value tomake up an index for designating the uniformity. It is clear from FIG. 7that higher the discharge pressure, the better the uniformity.

In consequence, inventors confirmed that the magnetron etching apparatusaccording to the first embodiment of the invention has successfullymaterialized an etching process which generated improved uniformity ofetching velocity and improved shape by processing resist with a minimumof 25 m Torr through a maximum of 125 m Torr of the etching gaspressure.

Next, in order to make sure of the effect of adding light-element gas tothe etching, inventors added helium to oxygen. FIG. 8 graphicallydesignates the distribution of etching velocity in the directionorthogonally intersection the line of magnetic force when applying astationary magnet. Curve (a) designates the etching gas composed ofgenuine oxygen, whereas curve (b) designates the etching gas composed of33% oxygen and 67% helium in blend. These curves respectively designatethe results of trial etching executed against semiconductor wafer having150 mm of diameter by applying 50 sccm of gas flow rate, 50 m Torr ofgas pressure, and 400 W OF RF power. As is clear from the comparisonbetween these curves (a) and (b), despite of the retarded etchingvelocity by about 5%, addition of helium gas to oxygen resulted in thenoticeably promoted uniformity of the etching effect. While the etchingprocess was underway using genuine oxygen gas by rotating the permanentmagnet, evenness of the etching was rated to be about 10%. However,addition of helium to oxygen promoted the etched effect by about 6%.

FIGS. 9A and 9B schematically designate sectional views of wafer samplescomplete with an etching process with the rotation of the permanentmagnet. The sectional view shown in FIG. 9A designates symptom ofconstriction occurred on the side wall by about 400 Å of the width. Onthe other hand, the sectional view shown in FIG. 9B designates thegouged edge by about 200 Å of the width, which is one-half thedissipated domain shown in FIG. 9A.

Because of negligible mass, even when helium molecules hit against thesubstrate, physical influence rarely takes place. Furthermore, helium ischemically stable, and therefore, helium does not directly affect theetching reaction. Despite of its own inertness, blend of helium gas andoxygen improves the uniformity of etching effect and the shape of theetched domain. This is probably because helium relaxes influence of thedeviant electron density inherent in the magnetron cathode-couplingsystem which is devoid of a closed circuit as in the dry etchingapparatus embodied by the invention.

Next, dimension of the wafer and electrodes and the relationship betweentheir dimensions and available material are described below. Themagnetron etching apparatus based on the first embodiment uses thoseelectrodes each having a certain radius wider by 15 mm than the waferhaving 75 mm of radius. These electrons surrounding the waferrespectively play important role to promote the evenness of the etchingvelocity. For comparative example, curve (c) shown in FIG. 6 designatesthe evenness of the etching velocity in the direction orthogonallyintersecting the line of magnetic force when providing those electrodesand the wafer with identical dimension. It is clear from the curve (c)that gradient of the etching velocity between both ends is extremelydifferential, thus indicating extremely poor uniformity of the etchingvelocity.

Next, representing another embodiment of the magnetron plasma processingapparatus of the invention, a method of executing the dry etching ofwafer by applying the dry etching apparatus based on thecathode-coupling system to the generation of gate electrode of a MOS LSIdevice is described below.

FIG. 10A schematically designates the sectional view of a wafer etchedby the magnetron plasma processing apparatus of the second embodiment ofthe invention. The wafer shown in FIG. 10A is produced by executingthose sequential processes including the following; formation of silicondioxide film having 100 Å of thickness on a silicon substrate 101 byapplying a thermal oxidation process; deposition of polycrystallinesilicon film 103 on the formed silicon dioxide film; doping phosphorusinto the deposited polycrystalline silicon film 103; and formation ofresist mask 109 on the phosphorus-doped polycrystalline silicon film103. Phosphorus-doped polycrystalline silicon film 103 is widely madeavailable for composing gate electrodes of MOS capacitors and MOStransistors, whereas silicon dioxide film 102 is made available for thedielectric material. When processing the polycrystalline silicon film103 in the structure mentioned above, uniformity and satisfactoryselectivity against the processable shape and the underlaid oxide film102 are compulsorily demanded. On the other hand, total protection ofthe insulating characteristic of the gate oxide film 102 against damageis compulsorily demanded. It is well known that, if the density ofplasma were unevenly distributed, then, intense electric field isgenerated in the gate oxide film 102 to easily result in the occurrenceof dielectric breakdown.

Inventors also carried out trials to check the relationship between thegas pressure gravely affecting the uniformity of the density of plasmaand the resistivity of the oxide film against gas pressure by applyingthe magnetron etching apparatus shown in FIG. 1 and chlorine etchinggas. Inventors supplied 150 W of high-frequency power to an electrodeand held the substrate at 0° C. Next, inventors executed an etchingagainst sample wafers before eventually producing MOS capacitors shownin FIG. 10B. Inventors then measured current-voltage characteristicbetween the substrate and the gate electrode made from polycrystallinesilicon film, and then, checked the faulty resistance rate againstapplied gas pressure. Table 1 designates the checked result.

                  TABLE 1                                                         ______________________________________                                        Pressure (×10.sup.-3 Torr]                                                             1      10     20   40   80   100                               ______________________________________                                        Reject rate    10     7      3    0    0    0                                 ______________________________________                                    

Inventors confirmed about 10% of the reject after applying 5 m Torr(5×10⁻³ Torr) of the gas pressure to the produced MOS capacitors. Thereject rate decreased to 7% after applying 10 m Torr of gas pressure.After raising the gas pressure to 40 m Torr and then beyond 40 m Torr,no reject occurred. This is because the higher the applied gas pressure,the better the uniformity of the plasma density, thus preventingelectric field from being generated in the gate oxide film 102 otherwisecausing reject to occur.

After critically checking the occurrence of destruction of gate,inventors detected that 25 m Torr of gas pressure was the critical limitto prevent the gate electrode from incurring destruction. Like theresist etching process mentioned above, inventors also confirmed thatthe uniformity of the etching velocity was also promoted relative to theincrease of the applied gas pressure.

Inventors also confirmed that higher the applied gas pressure, thehigher the selectivity against the oxide film from the test result whichyielded 20 of the selectivity at 40 m Torr and 35 of the same at 80 mTorr of gas pressure. On the other hand, inventors also detected thatundercut symptom was generated under the mask when the applied gaspressure was in excess of 160 m Torr.

Table 2 designates the relationship between the velocity applied to theetching of polycrystalline silicon film and silicon dioxide film and thesubstrate temperature. It is clear that the lower the substratetemperature, the better the selectivity. This effect is particularlynoticeable when the substrate temperature is below 0° C. In addition,the etched shape is improved by minimizing the undercut symptom.

                  TABLE 2                                                         ______________________________________                                                     Polycrystalline                                                               silicon film                                                     Temperature (°C.)                                                                   (Å/minute)                                                                            SiO.sub.2 film (Å/minute)                        ______________________________________                                        -30          2,800       30                                                   -15          3,000       50                                                   0            3,000       70                                                   15           3,000       100                                                  30           3,500       110                                                  ______________________________________                                         At 100 sccm of Cl.sub.2 gas flow; 75 m Torr of gas pressure; 100 W of RF      power                                                                    

Next, inventors replaced genuine chlorine gas with blend of 80% chlorineand 20% helium. After completing tests with the replaced blend gas,inventors confirmed that, owing to the function of helium ions whichhorizontally shielded electric field, critical pressure capable ofpreventing the tested film from incurring destruction lowered to 10 mTorr. Application of helium or any light-element gas componenteffectively expands the range of pressure to permit the system toprocess deposited film without incurring destruction.

Like the resist etching process methoned above, dimension of electrodesgravely affects the uniformity of the etching velocity.

FIG. 11 graphically designates characteristic of the velocity of etchingprocess applied to polycrystalline silicon film on the wafer surface byvarying the dimension of those electrodes of the magnetron plasmaetching apparatus shown in FIG. 1. Curve (a) designates the distributionof the etching velocity in the direction orthogonally intersectionmagnetic poles when using those electrodes each having radius 15 mmwider than that of the wafer. In contrast with the resist etching, theetching velocity is retarded in the leftward direction when electronsassemble themselves. Although the cause of this phenomenon is not yetclear, gradient is relatively mild. Curve (b) designates the result fromthe use of those electrodes having the dimension identical to that ofthe wafer, where the curve (b) indicates degraded uniformity of theetching velocity. Curve (c) designates the result from the use of thoseelectrodes having radius 15 mm wider than that of the wafer. Theseelectrodes were superficially covered with 2 mm thick quartz glass toprotect peripheral surface of these electrodes. Curve (c) indicatesextremely poor uniformity in contrast with curve (a). This is because,since the applied high-frequency electric field is distributed to boththe quartz sheet and the plasma sheath in peripheral edges of thoseelectrodes, electric field in the peripheral edges remains less thanthat is present on the wafer. Probability of destruction of gate risesin order of (a), (c), and (b). Therefore, in order to promote theuniformity of the etching velocity and prevent gate from incurringdestruction, it is essential for the system to use those electrodeshaving dimension greater than that of the wafer under process.

It is desired that the peripheral edges of these electrodes be composedof conductive material like metal or carbon up to the tip surface. If itis necessary to use insulating material to protect electrodes andprevent the wafer from incurring stain, it is essential for the systemto use selected insulating material having a maximum of 1 mm ofthickness.

Next, dry etching characteristic of those materials available forcomposing electrode is described below.

Chlorine gas is effectively applicable to the system for processing gateelectrodes of a MOS LSI device using the dry etching apparatus shown inFIG. 1. In addition, dry etching process can also be achieved to resultin the satisfactory shape of etched domain and satisfactory selectivityeven when using gas containing bromine like Br₂ or HBr in presence of aminimum of 10⁻² Torr of pressure. Amount of deposit can be minimized inthe course of the etching process by adding gas containing fluorine likeSF₆ to bromine gas, and as a result, satisfactory shape of the etchedobject can eventually be materialized.

Furthermore, the drying etching method embodied by the invention is alsoeffectively applicable to the manufacture of metallic silicide like Wsi,MoSi, or TiSi available for producing low-resistance electrodes. As wasproved in the above case, satisfactory shape of the etched domain andsatisfactory selectivity can also be achieved by applying gas containingeither chlorine, or bromine, or blend gas containing bromine orfluorine.

Silicon dioxide film serves itself as mask in the course of executing anetching process against a silicon substrate. Chlorine gas orbromine-contained gas is quite useful to secure selectivity against themasking silicon dioxide film. Inventors confirmed from the test resultthat, after executing an etching process against a silicon substrate byapplying blend gas composed of 90% Cl₂ and 10% SiCl₄, 10 through 50 mTorr of gas pressure, and 600 W of RF power, 15 of the selective ratiowas achieved against the etched silicon dioxide film. The etched shapewas dependent on the substrate temperature. The etched shape wasconfirmed to be vertical when the substrate temperature remained at 70°C. On the other hand, the etched shape was tapered in the forwarddirection when the substrate temperature remained at 50° C. Conversely,the etched shape was tapered in the backward direction when thesubstrate temperature was held in excess of 80° C. If the etched shapewere tapered in the backward direction, then, film interposing workinvolves much difficulty, and thus, it is suggested that the etchingprocess be executed while the silicon substrate contains a maximum of70° C. of temperature.

Although either HBr or Br₂ gas can be applied to the process for etchingthe silicon substrate, since deposit can easily be generated, it issuggested that bromine gas be blended with gas containing fluorine likeSP₆ for example.

After executing trial production of compound available for wiringmaterial containing aluminium, 1% silicon, and 2% copper by applyingblend gas containing 30% (or 70%) Cl₂ and 70% (or 30%) BCl₃ with 10through 80 m Torr of pressure and 200 W of RF power, inventors confirmedthat anisotropic etching effect free from undercut symptom wassuccessfully achieved. In presence of blend gas composed of 70% Cl₂ and30% BCl₃, inventors achieved 6,000 Å/minute of the etching velocity.Furthermore, the apparatus embodied by the invention can also execute anetching process capable of providing satisfactory anisotropy by applyingblend gas containing bromine like Br₂ or HBr₂ for example. In order toproperly execute an etching process against aluminium alloy, it issuggested that the substrate be heated to a certain degree above roomtemperature to prevent residue of the etching process from occurrence.

The apparatus embodied by the invention can also use CHF₃ gas to executean etching process against insulating materials including silicondioxide film, phosphorus-added silica glass, and boron-phosphorus addedsilica glass available for insulation. Table 3 designates therelationship between the etching condition, etching velocity, and theinclined angle of the side wall of the wafer.

                  TABLE 3                                                         ______________________________________                                                                           Etching                                    Pressure  Temperature                                                                              Tapered angle velocity                                   (m Torr)  (°C.)                                                                             (degrees)     (Å/minute)                             ______________________________________                                        5         20         82            3,500                                      10        20         75            2,700                                      40        20         67            4,100                                      5         60         88            3,600                                      10        60         82            3,700                                      40        60         75            4,200                                      ______________________________________                                    

At 50 sccm of CHF₃ and 600 W RF Power

The inclined angle of side wall tends to become narrow relative to therise of applied gas pressure and the decrease of substrate temperature.Based on these parameters, angle of incline can optionally beestablished.

Furthermore, the angle of incline expands when adding CF₄ gas, andconversely, the angle of incline contracts when adding CH₂ F₂ gas.Therefore, when properly adding these gas components, the angle of theinclined side wall can properly be controlled.

In the event that the available gas is compatible with a general formula"ClHmFn (m+n=2+2)", it can also be applied to the process for etchingsilica glass cited above.

As is clear from the above description, when processing resist andpolycrystalline silicon film by applying the etching method embodied bythe invention, uniformity of the etching velocity can be secured bystabilizing the pressure of etching gas at a minimum of 10 m Torr, andyet, occurrence of abnormally etched shape caused by uneven density ofplasma and damage incurring to gate oxide film can respectively beminimized.

The relationship between the applied gas pressure and the uniformity ofdischarge is not dependent on the kind of gas. In other words, inaddition to those embodiments thus far described, the magnetron etchingapparatus and the related method of the invention can securelymaterialized uniform effect of the etching process by applying theidentical pressure range based on the relationship between the waferunder process and a variety of etching gas applicable to the process foretching silicon dioxide film using ClHmFn(m+n=2+2) gas or applicable tothe etching of monocrystalline silicon film using bromine gas.

Furthermore, addition of helium gas to oxygen or chlorine results in thesharply promoted uniformity of the etching velocity and the shape of theetched domain, thus effectively suppressing destruction of gateelectrodes. This useful effect is generated by the degree of themovement of light-element ions. Identical effect can also be generatedby addition of hydrogen. Likewise, identical effect can also begenerated by applying compound gas containing HCl or HBr whose moleculesrespectively contain hydrogen.

The description of the above embodiment has solely referred to theexamples of processing resist, polycrystalline silicon film,monocrystalline silicon film, metallic silicide, silica glass, andaluminium alloy, respectively. However, the scope of the invention isnot merely limited to those materials cited above, but the scope of theinvention is also effectively applicable to the fine process of film forthe surface of a variety of materials including silica glass, aluminum,aluminum alloy, or copper, or tungsten, or other metals, as well.

Next, the relationship between the gas pressure in the vaccum chamber ofthe magnetron plasma etching apparatus shown in FIG. 1 and the etchingcondition is described below.

Line of magnetic force extending itself between those parallel planeelectrodes 22 and 24 is generated between external surfaces of thepermanent magnet 30 oh both sides in the magnetizing direction. Magneticfield containing about 100 G of magnetic entity is generated in domainadjacent to the wafer 14, where the magnetic field is generated inparallel with the upper surface of the wafer 14 and orthogonallyintersects electric field between those parallel plane electrodes 22 and24. Parallel magnetic field can uniformly be distributed on the wholesurface of the wafer 14 by effect of the rotation of the permanent maget30. While performing spining movement by way of pivoting the line ofmagnetic force of magnetic field in presence of parallel magnetic field,if electrons fly themselves in the tangential direction, then theseelectrons enter into the wafer 14 in the vertical direction. This inturn permits the magnetron plasma etching apparatus to properly executean etching process with satisfactory anisotropic effect against thewafer 14. After generating parallel magnetic field in the plasma sheathgenerated in the neighborhood of the wafer 14, inventors confirmed thatthe apparatus stably executed the etching process by generatingsatisfactory anisotropic effect.

The magnetron plasma etching apparatus embodied by the invention canachieve those advantageous effects described below by properlyestablishing gas pressure in the vacuum in a predetermined range from 10m Torr to a maximum of 100 m Torr. Unlike any conventional etchingsystem using several mTorr of gas pressure' gas pressure ranging from 10m Torr to a maximum of 100 m Torr applied to the etching process withthe magnetron plasma etching apparatus of the invention significantlyraises the probability of generating collision between ions of thesupplied gas component. This in turn strengthens the density of plasma,and therefore, as shown in FIG. 12, thickness of plasma sheath 52generated on the wafer 14 can be decreased. The wafer 14 discharges thesecondary electrons, and then, the discharged secondary electrons flythemselves in the direction orthogonally intersecting both the electricand magnetic fields by way of performing cyclonic movement until hittingagainst the wafer 14 to cause the wafer 14 itself to further dischargethose secondary electrons by incremental amount. Radius "r" of thecyclonic movement performed by those secondary electrons is determinedby the intensity of both the electric and magnetic fields. If the plasmadomain were closer to the wafer 14 then the radius "r", then thosesecondary electrons collide themselves with gas component of plasma,thus generating ionization. In consequence, the thinner the thickness ofthe plasma sheath 52, the greater the ionizing effect that can besecured. Based on this reason, as shown in FIG. 12, the apparatus cansecurely generate domain 54 containing intense density of plasma on thewhole surface of the wafer 14.

The magnetron plasma etching apparatus embodied by the invention cansecurely promote the etching rate itself and the uniformity of theetching rate by densely generating plasma domain 54 on the whole surfaceof the wafer 14.

As shown in FIG. 13, plasma sheath has substantial thickness whenseveral mTorr of gas pressure is present in the vacuum chamber, and as aresult, those secondary electrons performing cyclonic movement cannotoften traverse plasma domain 60 on the sheath 62. As a result, as shownin FIG. 13, those secondary electrons assemble themselves in specificregion 64 around the peripheral edges of the wafer 14. This in turnstrengthens the plasma density around the peripheral edges of the wafer14. This is the probable cause of degrading uniformity of the etchingrate in this sphere.

FIG. 14 graphically designates the distribution of the etching rate onthe wafer. The etching rate remains high and stably even when 30 m Torrof gas pressure is applied. On the other hand, etching rate remains lowand the uniformity is significantly degraded when merely applying 3.5 mTorr of gas pressure.

Next, extent of the improvement of the shape of the etched wafercomponent in correspondence with the gas pressure in the vacuum chamberis described below.

FIGS. 15A through 15D respectively designate the gouged symptomgenerated by applied gas pressure. Electron-assembled domain 64 is shownto the left. When 3.5 m Torr of gas pressure is applied, gouged regionis generated on on part facing the electron-assembled domain 64.Probably, this is because certain beams emitted from theelectron-assembled domain 64 hit against the gouged region. On the otherhand, when 10 m Torr of gas pressure is applied, the gouging symptomrarely takes place. Inventors further detected that no gouged region wasgenerated at all after applying 30 through 70 m Torr of gas pressure.The reference numeral 67 shown in FIG. 15A designates the domaincomplete with an etching process, whereas the reference numeral 68designates making member available for the etching process.

FIGS. 16A through 16C respectively designate the state of eliminatingcurve from the shape of the etched domain of the wafer 14. Afterapplying 3.5 m Torr of gas pressure, curve was generated on the sideopposite from the electron-assembled domain 64, in other words, on theSide where the effect of the etching process was low. Inventorsconfirmed that the curve symptom was substantially removed afterapplying 30 m Torr of gas pressure, and yet, no curve symptom wasgenerated after applying 30 m Torr of gas pressure.

FIG. 17 graphically designates the relationship between self-biasvoltage Vdc of the wafer 14 and gas pressure. As is clear from thisgraphic chart, the higher the gas pressure, the lower the self-biasvoltage Vdc. The self-bias voltage Vdc is substantially constant inpresence of 70 m Torr of gas pressure.

When the self-bias voltage Vdc is lowered, selective ratio sharing partof the etching characteristic is promoted. In addition, since differenceof the self-bias voltage Vdc on the wafer 14 can be decreasedprobability of generating damage like destruction of gate oxide film canbe diminished.

Next, the relationship between the direction of the line of magneticforce generated between those parallel plane electrodes 22 and 24 of themagnetron plasma etching apparatus embodied by the invention and theshape of the etched wefer component is described below. As shown in FIG.18, inventors carried out trial etching processes by obliquely disposingsample magnets 16a and 16b against those parallel plane electrodes 22and 24.

FIG. 19 graphically designates the tilted angle of the etched shape inthe center relative to the degree of incline θ of those sample magnets16a and 16b against the surface of those parallel plane electrodes 22and 24. When the inclined angle θ was less than 15 degrees, the tiltedangle of the etched shape was negligible. However, inventors detectedthat the tilted angle of the etched shape sharply expanded relative tothe expansion of the inclined angle θ beyond 15°. As a result, inventorsconfirmed that an ideal etching process with precise directivity couldbe materialized by contracting tilt angle between precisely set magneticfield and the wefer surface to less than 15 degrees, in other words, bycontracting the ratio of the vertical component of magnetic fieldagainst the horizontal component to less than tan 15°=1/4. Inventorsfurther confirmed from the test result that the permanent magnet 30introduced to the magnetron plasma etching apparatus of the inventionalso contained the vertical component of magnetic field in a range lessthan one-fourth the horizontal component.

Next, the detail of the magnetron plasma processing apparatus accordingto the second embodiment of the invention is described below. Note thatthose components of the apparatus identical to those which are providedfor the first embodiment are respectively designated by the identicalreference numerals. Therefore, description of these is deleted here.

The etching apparatus shown in FIG. 20 substantially being the magnetronplasma embodied by the invention is provided with the first electrode(the bottom electrode) 111 accommodating the wafer 14 on the uppersurface, the second electrode (the upper electrode) 112 which isopposite from the first electrode 111, and the third electrode 113 whichis concurrently with a ground reaction container. High-frequency poweris delivered to the first and second electrodes 111 and 112.

Initially, a high-frequency oscillator 114 outputs oscillatedfrequencies to an amplifier 115 for amplification, and thenhigh-frequency power is delivered to the first electrode 111 via animpedance matching box 116. On the other hand, oscillated frequenciesoutput from the high-frequency oscillator 114 is delivered to the otheramplifier 118 for amplification via a phase regulator 117, and thenhigh-frequency power is delivered to the second electrode 112 via theother impedance matching box 119. Since high-frequency power isdelivered to the first and second electrodes 111 and 112 from theidentical high-frequency oscillator 114, high-frequency power to bedelivered to both electrodes is held in a constant phasewiserelationship by the phase regulator 117, and thus, discharge is stablymaintained. The etching velocity can be maximized by optionallyregulating the phase relationship of supplied power.

The etching apparatus according to the second embodiment of theinvention properly regulates those amplifiers 115 and 118. As a result,self-bias voltage generated in the first and second electrodes 111 and112 can be set to an optional ratio. This in turn balances electronsperforming drifting movement on the upper and bottom electrodes topermit the apparatus to uniformly execute etching processes.

According to the composition of the magnetron plasma etching apparatusbased on the second embodiment, depending on materials subject to theetching process and the characteristic required for the etching process,the apparatus can freely set electric field that should be provided inthe neighborhood of those upper and bottom electrodes as an advantageousfeature. In consequence, the apparatus can precisely execute all theetching processes with satisfactory selectivity.

In place of the structure mentioned above, the second embodiment mayprovide the apparatus with a pair of high-frequency oscillators 114 inorder to feed high-frequency power containing different frequencies tothe first and second electrodes 111 and 112. For example, if either ofthese two high-frequency oscillators 114 provides the second electrode112 with a certain high-frequency voltage beyond the capability of ionsto follow up and the other high-frequency oscillator 114 provides thefirst electrode 111 with a low-frequency voltage, then, the apparatuscan selectively execute an etching process against the wafer 14 mountedon the first electrode 111 by way of effectively preventing the materialof the second electrode 112 from wearing itself.

FIG. 21 schematically designates the magnetron plasma processingapparatus according to the third embodiment of the invention. Note thatthose components identical to those which are shown in FIGS. 1 and 20are designated by the identical reference numerals. Therefore,description of these components is deleted.

In place of directly feeding high-frequency voltage to the secondelectrode 112, the magnetron plasma processing apparatus according tothe third embodiment directly connects a variable inductor 122 and acapacitor 121 to the second electrode 112 in series, where the inductor122 and the capacitor 121 are respectively grounded as shown in FIG. 21.The magnetron plasma etching apparatus preliminarily selects both thecapacitor 121 and the inductor 122 in order that serial resonantfrequency of the capacitor 121 and the inductor 122 can substantiallymatch the frequency output from the high-frequency oscillator 114.

The capacitor 121 insulates the second electrode 112 using DC component.Phase of high-frequency voltage induced to the second electrode 112 canproperly be adjusted by regulating the inductor 122, and thus, self-biasvoltage generated on the surface of the second electrode 112 can also beadjusted. As a result, as was done for the second embodiment, driftingmovement performed by electrons on the upper and bottom electrodes canproperly be balanced to permit the apparatus to uniformly execute theetching processes. When the phase of high-frequecy voltage delivered tothe second electrode 112 is properly adjusted, plasma assemble in thecenter of the second electrode 112 to promote density of plasma in thecenter of this electrode, and conversely, plasma can also be dispersedto the peripheral edges of this electrode.

It is desired that the impedance of the capacitor 121 and the inductor122 connected to the second electrode 112 be correctly identical to theimpedance of the high-frequency oscillator 114. Although ground wire isconnected to the third electrode 113, since the third electrode 113contains impedance, induced voltage is partly generated, thus providinga certain potential for the third electrode 113.

When operating the magnetron plasma etching apparatus of the thirdembodiment, self-bias voltage generated on the surface of the upperelectrode 112 has such a variable range which is narrower than that isprovided for the apparatus of the second embodiment. On the other hand,owing to relatively simple structure, the apparatus based on the thirdembodiment can be manufactured at inexpensive cost.

The magnetron plasma etching apparatus of the third embodiment may usesuch an inductor 122 containing a preliminarily optimized stationaryvalue. In place of the structure mentioned above, the apparatus of thethird embodiment can also feed high-frequency voltage to the secondelectrode 112, and in addition, the apparatus can insert the capacitor121 and the variable inductor 122 between the first electrode 111 andthe ground terminal.

Next, an example of the variation of the permanent magnet 30 of themagnetron plasma etching apparatus is described below. As shown in FIG.22, the permanent magnet 30 of the modified version consists of a mainmagnet 130, a non-magnetic member 132, and a counter magnet 134. Asshown in FIG. 23 for example, the main magnet 130 is substantially arectangular permanent magnet having plural steps on both sides. The lineof magnetic force is provided across the N-pole and the S-pole in thedirection orthogonally intersecting the longitudinal axial direction ofthe main magnet 130. A plane recess 130a is provided in the center ofthis main magnet 130, where the main magnet 130 is secured right abovethe upper surface of the vacuum chamber 20 by way of pronely disposingthe plane recess 130a in order that part of magnetic flux can penetratethrough the plasma atmosphere in the vacuum chamber 20.

The counter magnet 134 is provided on the main magnet 130 via thenon-magnetic member made from aluminium or resinous material. Thecounter magnet 134 is provided with specific strength identical to thatof the main magnet 130 (where the strength may not necessarily beexactly identical to each other) and the structure exactly identical tothat of the main magnet shown in FIG. 23. The main magnet 130 and thecounter magnet 134 are respectively provided with phases which areelectromag-netically and physically opposite from each other by 180°.For example, opposite magnetic poles are disposed in opposition fromeach other as shown in FIG. 22.

A motor 136 is connected to the center plane recess 134a of the countermagnet 134 via a rotary shaft 36. The motor 136 rotates the permanentmagnet 30 which is composed of the main and counter magnets 130 and 134.

Since these main and counter magnets 130 and 134 are vertically disposedby way of aligning opposite magnetic poles in opposition from eachother, magnetic flux generated from the N-pole of the main magnet 130 onthe part of the counter magnet 134 is attracted by the S-pole of thecounter magnet 134, and conversely, magnetic flux generated from theN-pole of the counter magnet 134 on the part of the main magnet 130 isattracted by the S-pole of the main magnet 130. This in turn decreasesthe amount of magnetic flux orthogonally hitting against a shield 140secured to the base of the apparatus by way of covering the permanentmagnet 30, thus promoting the shielding effect of the shied 140 itself.

When the main magnet 130 is solely provided for the apparatus as shownin FIG. 24, magnetic flux diffusing in the direction orthogonallyhitting against the sheild 140 permeates through the shield 140, thuslosing own shielding effect of the shield 140 itself. Additionalprovision of the counter magnet 134 causes opposite magnetic poles ofthe main and counter magnet 134 and 134 to attract each other, thusdecreasing the amount of leaked magnetic flux and promoting theshielding effect of the shield 140 itself.

The main and counter magnets 130 and 134 composing the permanent magnet30 shown in FIG. 22 is coupled with each other via the non-magneticmember 132. In place of this triple composition, as shown in FIG. 25,the main and counter magnets 130 and 134 may directly be coupled witheach other across a vertically erected rotary shaft 42.

FIG. 26 graphically designates the distribution of magnetic field on thewefer 14 when the main magnet 130 is solely made available for composingthe permanent magnet 30 and when both the main and counter magnets 130and 134 are conjunctionally made available for composing the permanentmagnet 30. The curve with round symbols designates the distribution ofmagnetic field when the main magnet 130 is solely made available,whereas the curve with square symbols designates the distribution ofmagnetic field when the main and counter magnets 130 and 134 areconjunctionally made available.

As shown in FIG. 27, the horizontal axis designates the distance fromthe center of the main magnet 130, in other words, from the center ofthe wafer 14. On the other hand, the vertical axis designates thedensity of magnetic flux. The reference character "Bx" shown in FIG. 26designates horizontal component (component X) of the density of magneticflux at respective local points apart from the center position "0" ofthe wefer 14. On the other hand, the reference character "Bz" shown inFIG. 26 designates vertical component (component Z) of the density ofmagnetic flux in those corresponding points.

It is clear from the graphical chart shown in FIG. 26 that, even whenthe counter magnet 134 is provided, magnetic field applied to the wafer14 in the vacuum chamber 20 substantially remains constant.

FIG. 29 graphically designates the result of analyzing the leakedmagnetic flux (horizontal component) relative to the distance L (seeFIG. 28) from the center of the main magnet 130 or the center of thecounter magnet 134 when the main magnet 130 is solely provided and alsowhen the counter magnet 134 is conjunctionally provided for composingthe permanent magnet 30.

As is clear from the graphical chart shown in FIG. 29, when the countermagnet 134 is conjunctionally provided, the analyzed value indicatesthat there is no substantial difference in the amount of leaked magneticflux when the distance L is several times less than the diameter ofthose available magnets. On the other hand, when the diameter L isseveral times longer than the diameter of those available magnets, thedifference between the amount of leaked magnetic flux when solelyapplying the main magnet 130 and the amount of leaked magnetic flux whenconjunctionally applying the main and counter magnets 130 and 134gradually expands.

FIG. 30 graphically designates the result of analyzing the leakedmagnetic flux at a points which is horizontally apart from the center ofthe counter magnet 134 by a predetermined distance after varying thedistance H between the main and counter magnets 130 and 134 againstdiameter R of these magnets made available for the counter magnet system(see FIG. 31). It is clear from these graphical charts that the longerthe distance H between both magnets, the greater the amount of leakedflux which is linearly incremental at the predetermined point P. Inother words, the shorter the distance between the main and countermagnets 130 and 134, the less the amount of leaked magnetic flux.

FIG. 32 graphically designates the variation of the density of magneticflux at the center of the wefer 14 relative to the variation of thedistance H between the main and counter magnets 130 and 134 availablefor the counter magnet system. Even when the counter magnet 134 is closeto the main magnet 130, density of magnetic flux at the center of thewefer 14 mildly decreases.

The above description on the modification of the permanent magnet 30 hassolely referred to the case in which those main and counter magnets 130and 134 are respectively and substantially the permanent magnet 30.Alternatively, either or both of these magnets may be composed ofelectromagnet. In either case, it is essential for the apparatus of theinvention to uniformly generate magnetic field in parallel with thesurface of the wafer 14 and provide an appropriate means for generatingsuch magnetic field oriented in the direction 180° apart from that ofthe horizontal magnetic field in parallel with the surface of the weferso that this horizontal magnetic field can fully be offset.

The above description has referred to a variety of embodiments of theinvention covering the magnetron plasma processing apparatus and themethod of properly executing dry etching process against semiconductorwafers using this apparatus. As far as magnetron plasma is securely madeavailable, the scope of the invention may also effectively be applied tothose surface processing apparatuses available for executing chemicalvapor deposition process or sputtering process or the like.

It should be understood that the invention is not merely confined tothose embodiments and modifications thus far described, but theinvention may also be embodied and modified in a variety of useful wayswithout substantially departing from the spirit and scope of theinvention.

What is claimed is:
 1. A magnetron plasma processing apparatuscomprising:a vacuum chamber which stores an etching object; a pair ofparallel electrodes respectively provided in said vacuum chamber andhaving a first electrode holding said etching object and a secondelectrode being opposite from said first electrode; a third electrodewhich surrounds said first electrode and is grounded; gas-supply meansfor supplying gas to said vacuum chamber; magnetic-field generatingmeans, which is opposite from said first electrode in opposition fromsaid second electrode, the magnetic field generation means having aconfiguration for generating a magnetic field parallel with the uppersurface of said etching object between said pair of parallel planeelectrodes; means for rotating the magnetic field generating means torotate the magnetic field; and power-supply means for supplying power toat least either of said first and second electrodes and generatingdischarge between said pair of parallel plane electrodes; wherein saidpower-supply means has means for supplying power to said first andsecond electrodes.
 2. A magnetron plasma processing apparatuscomprising:a vacuum chamber which stores an etching object; first andsecond electrodes positioned in the vacuum chamber in a parallelrelationship, the first electrode supporting said etching object, a topsurface of said etching object facing the second electrode; ahigh-frequency power source for outputting an oscillating output; ameans for supplying the oscillating output outputted from thehigh-frequency power source to the first and second electrodes,respectively; and means provided to the supplying means, for adjusting arelative phase of the oscillating output supplied to the first andsecond electrodes, to maintain a stable discharge between the first andsecond electrodes.
 3. A magnetron plasma processing apparatus accordingto claim 2, wherein said supplying means comprises:a first connectingmeans for electrically connecting the high-frequency power source to thefirst electrode, and a second connecting means for electricallyconnecting the high-frequency power source to the second electrode; andsaid phase adjusting means provided to the second connecting means foradjusting phase of oscillated frequency supplied to the secondelectrode.
 4. A magnetron plasma processing apparatus according to claim3, which includes impedance matching circuits respectively provided tothe first and second connecting means.
 5. A magnetron plasma processingapparatus according to claim 4, which includes amplifiers respectivelyprovided to the first and second connecting means.